The present application is based on and claims priority from Japanese Patent Application Nos. HEI 11-148289 filed on May 27, 1999, HEI 11-170186 filed on Jun. 16, 1999, and 2000-89084 filed on Mar. 28, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a wheel with a damper for an automobile and the manufacturing method therefor.
2. Description of Related Art
In recent years, improving automobile fuel economy is important from the standpoint of protecting the global environment, and decreasing tire rolling resistance is strongly demanded. Among various resistance decreasing means, means for suppressing energy loss due to deformation of the side wall portion of the tire is effective. Accordingly, adoption of a highly pressurized tire and a low-profile tire which is low in height and has a small differential between an inside diameter and an outside diameter is increasing.
However, there are the following problems associated with a tire which is suppressed in deformation at the side wall portion, because a role a normal tire plays in suppressing a vibration transmission from a road to an automobile body decreases:
{circle around (1)} Ride quality lowers to cause a so-called bumpy feeling. The reason is that vibration in a vertical direction in the range of 10 Hz or higher is damped only a little compared with the case of a normal tire.
With an automobile mounted with a normal tire, vibration in the range of 10-12 Hz or higher is absorbed or damped by the tire, and vibration lower than 10-12 Hz including a floating and tilting feeling of the range of 5 Hz or less and vibrating feeling of the range of 5-12 Hz is absorbed or damped by a suspension system. However, with the highly pressurized tire and the low-profile tire, since the stiffness of the tire in the vertical direction increases, vibration in the range 10-30 Hz is slightly damped.
Japanese Patent Publication HEI 5-338401 proposes a wheel where a vibration insulating rubber is disposed between a rim and a disk. In the proposed wheel, the rubber acts as a vibrational barrier for insulating vibration due to the viscosity or viscous elasticity of the rubber, and therefore, the rubber does not act as a spring damper. Further, the rubber acts in compression and has too high spring constant to effectively damp the above-described bumpy feeling. With almost all of the other proposed wheels having a vibration insulating rubber disposed between a rim and a disk, the rubber is intended to act in compression and is too hard to effectively damp the bumpy feeling.
{circle around (2)} For the same reason as above, road noise (a noise hearing as xe2x80x9czaaxe2x80x9d when a automobile runs on the road) increases. A vibration generated due to the road surface is transmitted to the body and vibrates the body panel to generate the road noise. Though the frequency range where the road noise appears changes according to a respective automobile, the road noise tends to appear in the range of 50-500 Hz from the general structure of an automobile. The road noise becomes particularly large in the vicinity of 250 Hz where the tire generates a columnar resonance.
{circle around (3)} Problems of instability in controllability arise.
More particularly, with a tire having a high rigidity at its tread such as a wide tire, the camber thrust force is small and the wheel tends to be drawn into a slanted portion of the road such as a wheel track. With a normal tire, since the gravitational force for drawing the wheel into the wheel track is negated by the camber thrust force, falling of the wheel into the wheel track does not tend to occur. Contrarily, with the tire having a high rigidity at its tread, since the tire tread is not easily deformed to the slant of the wheel track, the camber thrust force is too small to cancel out the effect of the gravitational force, so that falling of the wheel into the wheel track of the road easily occurs.
Further, with the conventional wheel where the rim and the disk are rigidly connected to each other, the road gripping force of the tire during rolling of the automobile decreases. When the automobile rolls due to a rapid turn, the automobile transversely inclines and a camber angle is generated between the automobile and the road surface. At the same time, the rim inclines and the tire inclines, and as a result, the road contact pressure of the tire becomes non-uniform in the width direction of the tire, and the road gripping force decreases. Thus, the force counteracting the centrifugal force also decreases, and despite efforts to steer the automobile during turning, the automobile tends to slip straight ahead. Conventionally, this slippage is prevented by the suspension system. However, when the rolling is large, the slippage cannot be prevented by the suspension system only.
Further, with the high performance tire such as a wide tire, a sudden ability to steer the automobile is likely to occur. A rising angle of the yaw rate (the yaw speed versus steering angle) of the high performance tire is large compared with that of the normal tire. Thus, with the high performance tire, steering suddenly works after a predetermined ineffective steering angle. If the high performance tire is mounted to the automobile which has been tuned for mounting the normal tire, the gain of steering is too great for the automobile to be steered, and a steering problem arises.
{circle around (4)} For compensating the imbalance and uniformity of the wheel, mounting a balancing weight to the wheel and the balancing the wheel are necessary.
{circle around (5)} With the wheel mounted with a rubber member between the rim and the disk, safety when the rubber member breaks should be maintained. Therefore, even if the rubber member breaks, the rim and the disk should not separate from each other, and even if even if the rubber member breaks, the rim and the disk should be able to transmit a drive torque and a brake torque between them. With almost all of the proposed wheels having the rubber member disposed between the rim and the disk, when the rubber member breaks, the drive torque and the brake torque are not transmitted between the rim and the disk any more. Therefore, such proposed wheels cannot be practically used.
An object of the invention is to provide a wheel with a damper for an automobile which can improve a ride quality.
Another object of the invention is to provide a wheel with a damper for an automobile which can suppress road noise as well as improve a ride quality.
Another object of the invention is to provide a wheel with a damper for an automobile which can improve steering controllability as well as ride quality.
Another object of the invention is to provide a wheel with a damper for an automobile which can attain self-alignment of the tire mounted wheel as well as improve ride quality.
Another object of the invention is to provide a wheel with a damper for an automobile which enables the automobile to operate safely for some distance even when a rubber member disposed between a rim and a disk breaks, as well as improve ride quality.
Another object of the invention is to provide a method for manufacturing with high productivity a wheel with a damper for an automobile capable of improving a ride quality.
The above objects can be performed by a wheel with a damper for an automobile and a method for manufacturing the same according to the invention as follows:
(1) A wheel with a damper for an automobile according to the present invention includes: a rim, a disk radially spaced from the rim, and a damper disposed between the rim and the disk. The damper has a rubber member having a spring constant. The spring constant of the rubber member of the damper is determined such that a first natural frequency of a vibrational system with a spring of the rubber member and a mass of the automobile is in a range of 6-12 Hz.
Preferably, the above wheel with a damper is constructed as follows:
(2) In the wheel with a damper of (1), the spring constant of the rubber member of the damper is selected such that the first natural frequency of the vibrational system with a spring of the rubber member and a mass of the automobile is in a range of 8-10 Hz.
(3) In the wheel with a damper of (1), a spring constant of the rubber member of the damper is determined such that a first natural frequency of a vibrational system with a spring of the rubber member and a mass of the rim positioned radially outside of the rubber member is in a range of 50-200 Hz.
(4) In the wheel with a damper of (3), the spring constant of the rubber member of the damper is selected such that said first natural frequency of the vibrational system with a spring of the rubber member and a mass of the rim is in a range of 70-150 Hz.
(5) In the wheel with a damper of (1), the rim is a rim for mounting a low-profile tire or a highly pressurized tire thereon.
(6) In the wheel with a damper of (1), the rubber member of the damper includes a first portion which causes mainly an elastic shear deflection to act as a spring when the rim and the disk cause a relative displacement to each other in a vertical direction.
(7) In the wheel with a damper of (1), the rubber member of the damper includes a second portion which is brought into contact with an opposing member to act as a stopper when the rim and the disk cause a greater relative displacement to each other in a vertical direction than a gap between the second portion and the opposing member.
(8) In the wheel with a damper of (1), the damper includes: a rim side member which is pushed against or connected to or fixed to or integrally formed with the rim, and a disk side member which is pushed against or connected to or fixed to or integrally formed with the disk. The damper includes a first portion having opposite ends. The first portion is fixed to the rim side member at one of the opposite ends and to the disk side member at the other of the opposite ends. A smallest diameter of the rim side member is smaller than a largest diameter of the disk side member so that the rim side member and the disk side member are impossible to separate from each other in an axial direction of the wheel.
(9) In the wheel with a damper of (6), the first portion of the rubber member includes a first end surface where the first portion is fixed to the rim or a rim side member fixed to the rim and a second end surface where the first portion is fixed to the disk or a disk side member fixed to the disk. The first end surface and the second end surface of the first portion of the rubber member extend perpendicularly to an axis of the wheel.
(10) In the wheel with a damper of (6), the first portion of the rubber member includes an inside surface and an outside surface which contact a space and are a free surface.
(11) In the wheel with a damper of (6), the first portion of the damper extends in an axial direction of the wheel or with an angle less than 10 degrees to an axis of the wheel when no load acts on the damper.
(12) In the wheel with a damper of (6), the rubber member is constructed of rubber or a laminate of rubber plates and metal plates or a metal-wire-embedded rubber.
(13) In the wheel with a damper of (6), the first portion of the rubber member is fixed to the rim or a rim side member fixed to the rim and to the disk or a disk side member fixed to the disk by vulcanization adhesion.
(14) In the wheel with a damper of (6), the first portion of the rubber member is fixed to the rim or a rim side member fixed to the rim and to the disk or a disk side member fixed to the disk by a mechanical fixing. In the mechanical fixing, a surface of the rim or the rim side member for fixing the rubber member is knurled and a surface of the disk or the disk side member for fixing the rubber member is knurled. The rubber member is pressed in an axial direction of the wheel against the knurled surfaces to engage the knurled surfaces.
(15) In the wheel with a damper of (7), a space is provided between the second portion of the rubber member of the damper and an opposing member which the second portion opposes. A size of the space in a radial direction of the wheel is selected to be 2d+xcex1, where d is a deflection of the damper when a gravitational force of the automobile acts on the damper, and xcex1 is a value in a range of 0-1 mm.
(16) In the wheel with a damper of (7), the second portion of the rubber member is fixed by vulcanization adhesion to either one of the rim or a rim side member fixed to the rim and the disk or a disk side member fixed to the disk.
(17) In the wheel with a damper of (8), the rim side member is fixed to the rim by a first weld and the disk side member is fixed to the disk by a second weld. A position and a kind of the first weld and the second weld are selected such that a weld conducted after vulcanization adhesion of the rubber member for assembly does not give a damage due to welding heat to the rubber member.
(18) In the wheel with a damper of (8), the rim side member includes two sub-members. One sub-member of the two sub-members is pressed against said rim without being welded to the rim, and the other sub-member of the two sub-members is welded to the rim.
(19) In the wheel with a damper of (1), the rim is made from steel or wrought aluminum or cast aluminum or synthetic resin or fiber reinforced polymer.
(20) In the wheel with a damper of (1), the disk is made from steel or wrought aluminum or cast aluminum or synthetic resin or fiber reinforced polymer.
(21) In a method for manufacturing a wheel with a damper of (1), the method includes: casting a rim and disk integral product, cutting the product into two parts to obtain the rim and the disk; and mounting the damper between the rim and the disk to obtain the wheel with a damper.
With a wheel according to any of the above (1)-(20), since the first natural frequency of the vibrational system with a spring of the rubber member and a mass of the automobile is in the range of 6-12 Hz, vibration in the range slightly higher than the first natural frequency is damped so that the bumpy feeling is suppressed and ride quality is improved. When the resonance point of the vibrational system is set at slightly below 10 Hz, the bumpy feeling in the range of 10-30 Hz is absorbed and damped.
Further, since the damper has a soft structure, the tire inclines due to the deflection of the damper. As a result, the camber thrust force is large, and falling of the wheel into the wheel track is prevented. Further, when a camber angle is caused to the wheel due to rolling of the automobile, the rim inclines to be along the road, so that the road contact pressure of the tire is uniform, and the road holding characteristic of the tire is improved. As a result, the controllability during a turn becomes stable. Further, since the damper has a soft structure, there is a time lag in steering, so that a sudden ability to steer a car is modified, and controllability is improved.
Further, since the damper has a soft structure, the tire-mounted wheel has a self-aligning function. Namely, the tire-mounted wheel functions to select a center of rotation by itself and to rotate, and it becomes unnecessary to mount a balancing weight for compensating an imbalance of the tire-mounted wheel to the tire-mounted wheel. Thus, balancing work becomes unnecessary.
With a wheel according to any of the above (3) and (4), since the first natural frequency of the vibrational system with a spring of the rubber member and a mass of the rim is in the range of 50-200 Hz, vibration in the range slightly higher than the first natural frequency is damped so that vibration transmissibility in the range of 150-500 Hz is suppressed, and road noise is decreased.
With a wheel according to any of the above (6) and (9)-(14), since the rubber member acts in a shear deflection, the first portion can act as a soft spring having a low spring constant, the first natural frequency of the vibrational system with a spring of the rubber member and a mass of the automobile can be easily tuned in the range of 6-12 Hz.
With a wheel according to any of the above (7), (15) and (16), since the stopper rubber member is provided, even if the first portion of the rubber member breaks, the automobile can still operate due to the torque transmittance between the stopper rubber member and the opposing member.
With a wheel according to any of the above (8), (17) and (18), since a smallest diameter of the rim side member is smaller than a largest diameter of the disk side member, the rim side member and the disk side member cannot separate from each other in the axial direction of the wheel. Therefore, even if the rubber member of the damper breaks, the breakage is a fail-safe.
With the manufacturing method of a wheel according to (21), since the rim and the disk are integrally cast and then the cast is cut into the rim and disk, productivity is improved compared with the case where the rim and the disk are cast separately.